1. Field of the Invention
The invention relates to a control apparatus and a control method for a transmission-equipped hybrid vehicle having an engine, an electric motor, and a transmission. More particularly, the invention relates to a control apparatus and a control method that improve fuel efficiency, emission characteristics, dynamics, etc.
2. Description of Related Art
A hybrid vehicle has an engine and an electric motor as drive power sources. The electric motor is preferably used not only to produce vehicle-driving torque but also as an electric power generator. In this respect, the electric motor is often termed motor-generator. The hybrid vehicle is able to improve fuel economy and the like by efficiently operating the engine and the electric motor.
A mechanical distribution type hybrid vehicle in which an engine and two electric motors are connected to a planetary gear unit has now been commercialized. This type of hybrid vehicle does not have a transmission. In contrast, a hybrid vehicle in which an engine, an electric motor, and a transmission are connected has also been proposed, as disclosed in, for example, Japanese Laid-Open Patent Application No. 8-168104. Systems equipped with continuous transmissions instead of stepwise transmissions (a type of transmission that selects one of a plurality of gear speeds) have also been proposed.
In the aforementioned mechanical distribution type hybrid apparatus, optimization in terms of fuel economy and the like is pursued by controlling the operation states of the engine and the electric motors. However, this type of hybrid apparatus does not have a transmission for selecting from gear speeds.
With regard to a vehicle that is not a hybrid vehicle, speed change characteristics of the automatic transmission are set so as to correspond to the vehicle speed and the amount of accelerator operation. Based on the speed change characteristics, a gear speed of the transmission is determined. A generally termed MMT (multi-mode manual transmission, that is, a transmission system where a clutch pedal is removed and clutch connecting/disconnecting operations are automatically performed by an actuator) also uses the speed change characteristics of the automatic transmission in a similar fashion to determine a gear speed.
A transmission-equipped hybrid vehicle as mentioned above can be constructed by adding to a system in which an engine and a transmission are connected as mentioned above, an electric motor that produces torque to add to the drive power of the engine. However, if the speed change characteristics of an automatic transmission intended only for use with a conventional engine are immediately applied to the transmission-equipped hybrid vehicle although the electric motor is added to the hybrid vehicle, it is impossible to select a gear speed that allows most efficient operation, and it is difficult to perform appropriate controls regarding efficiency, emissions, vehicle dynamics, etc.